In the development of a semiconductor device, elements are further integrated; each element is made smaller and an operating voltage is reduced. For example, in the field of an advanced DRAM (Dynamic Random Access Memory) device, the shrinking of the size of a memory cell leads to a limited space occupancy for capacitors that make up a memory cell. If the capacitors do not have enough capacitance, the memory cell is prone to malfunctioning as the electric charge of the capacitors decreases due to noise signals from the outside and the like. Such malfunctions trigger errors, one typical example of which is a soft error.
In general, the capacitance of the capacitors that make up the memory cell of the DRAM device is in proportion to a surface area of an electrode and a relative permittivity of the dielectric substance and in inverse proportion to the distance between electrodes. In order to realize capacitors of a memory cell required to make the advanced DRAM device, it is necessary to use a dielectric film that has a high relative permittivity and can be made thin without an increase in leakage of current.
The use of HfO2, ZrO2 and Al2O3 is examined as means for increasing the capacitance of the capacitors of the DRAM: HfO2, ZrO2 and Al2O3 have higher relative permittivities than a conventional capacitance insulation film such as a SiO2 film, a SiN film or a SiON film, which is a combination of both. Recently, in order to reduce an increase in leakage of current associated with a thinner capacitance insulation film, research has been conducted on a capacitance insulation film generated by doping a laminated structure of HfO2, ZrO2 and Al2O3 or HfO2 and ZrO2 with a metal element. Development is under way to improve the electrical properties of the capacitors through the optimization of electrode materials that make up the capacitors.
For example, PTLs 1 and 2 show capacitance insulating materials generated by doping HfO2 and ZrO2 with such metal elements as aluminum (Al), scandium (Sc) and lanthanum (La). PTLs 1 and 2 state that the doping of HfO2 and ZrO2 with the above metal elements changes an electron affinity of an dielectric material as well as the barrier height of electrons and positive holes, and that an amorphous dielectric material tends to be formed as the formation of a crystal structure decreases or vanishes due to the existence of doping metals. PTLs 1 and 2 state that the relative permittivity of the dielectric material is anywhere between 10 and 25.
What is disclosed in PTL 3 is an amorphous film that has a crystal dielectric substance to which amorphous aluminum oxide is added as a capacitance insulation film and is made with AlxM(1-x)Oy (M represents a metal that can form a crystal dielectric substance such as Hf or Zr) with the composition 0.05<x<0.3. A feature of the technique is to prevent the breaking of insulation of the capacitance insulation film while keeping a high relative permittivity of 25 to 28 with amorphous zirconium aluminate. PTL 3 states that the relative permittivity of ZrO2 is 30.
NPL 1 states that an amorphous ZrO2—Al2O3 thin film, made by magnetron sputtering, crystallizes and thus has a tetragonal or monoclinic crystal structure when being annealed at 1,000 degrees Celsius. According to NPL1, the amorphous ZrO2—Al2O3 thin film crystallizes into a monoclinic crystal structure when the atom ratio of Zr to Al is 76:24; a tetragonal crystal structure is dominant when the atom ratio is 52:48. However, the value of relative permittivity is not disclosed.
PTL 4 states that in a capacitor having a capacitance film composed of ZrO2, as for the composition ratio of a TiN electrode that makes up an upper electrode, when titanium is set at 100% in atom ratio, carbon comes to 25 to 36%, nitrogen to 60 to 72%, and oxygen to 28 to 35% in order to prevent the deterioration of electrical properties associated with plasma treatment.